As a population of mice reaches optimum density the relations among members of each subgroup are examined with respect to pair bonding, acquisition of social roles and the development of social velocity and dominance hierarchies. In such contexts rodent vocalizations and their temporal variations are examined with particular emphasis on frequency, duration and amplitude. Vocal patterning exhibited by mice in optimum-sized groups will serve as a base line for judging the degradation of capacity for vocal communication that developes with crowding. This project includes part of discontinued projects ZO1 MH 00828, 29, and 30. BIBLIOGRAPHIC REFERENCES: Calhoun, J.B.: Crowding and Social Velocity. In: Arieti, S. and Chrzanowski, G. (Eds.): New Dimensions in Psychiatry. New York, John Wiley Sons, 1977, pp. 27-45. Deitchman, R., Sanders, R.E., Burkholder, J.H., and Newman, I.: Effects of prenatal crowding on rodent maternal and offspring behavior. Psychological Reports. 40: 327-338, 1977.